Many peptides and proteins have biological activity, which can be used as potential therapeutics. Delivery of these peptide/protein drugs is one of the biggest obstacles to clinical application. Taking advantage of the PRINT technology, we are exploring how to deliver peptide/protein drugs into cells and maintain the drugs’ biological activity.

Poly(L-lactic acid) (PLLA) and Poly(lactic acid-co-glycolic acid) (PLGA), first used for sutures, have more recently received attention as drug delivery matrices. PLLA and PLGA are bioabsorbable polymers that degrade hydrolytically at physiological pH and are then metabolized by the Krebs cycle. This makes them very attractive for drug delivery because there are no residuals after treatment. Both PLLA and PLGA particles are, for the most part, currently fabricated by either emulsion solvent evaporation methods or supercritical processing techniques. With these methods, spherical particles are generated, and while there is some basic control over size, the particles created are disperse. Encapsulation of cargos is also a challenge with these methods because the cargo typically has some affinity for the secondary phase and partitions out of the polymer phase before solidification. Finally, these methods tend to be water and/or solvent intensive, which is harmful for the environment and increases processing costs. Using the PRINT platform, we have developed new, cleaner methods for making bioabsorbable particles with complete control over size and shape. These particles can be surface functionalized and can easily encapsulate a wide variety of cargos. Currently we are looking at these particles for delivery of biological cargos such as antisense oligonucleotides.

This research involves the nano-molding of proteins for the fabrication of protein PRINT particles of monodisperse size and shape. Lyophilized protein particles are generally highly dispersed in particle size, aggregated, and often made through costly and complicated processes. Attempts to engineer monodisperse, discrete protein particles using wet-milling, spray-freeze-drying, microemulsion, or super critical fluid methods have realized little success. The PRINT technology enables a gentle, facile route to monodisperse particles of 100% protein as small as 200 nm cylinders. Protein PRINT particles of any shape and size are effortlessly achievable. Our research efforts include making PRINT particles composed of albumin and albumin 0.5 wt % siRNA, and Abraxane, the gold standard therapeutic used in metastatic breast cancer.

Figure 1. MicroPET imaging with 64Cu-DOTA PRINT particles. Time resolved PET images consisting of a two hour dynamic scan. The PET/CT images are overlayed. Mouse was injected with 136.2 µCi of 64Cu-labeled DOTA-nanoparticle. Both the coronal view (top), and sagittal view (bottom) are presented.

We have successfully designed PRINT particles that can be conjugated to 64 Cu, a long-lived positron emitter useful for micro-PET/CT imaging. This work, in collaboration with the Stanford Center for Cancer Nanotechnology Excellence Focused on Therapy Response and the CalTech/UCLA/Institute for Systems Biology Nanosystems Biology Cancer Center, allows us to monitor the biodistribution of our PRINT particles in vivo, in real time. Currently the group is working on the incorporation of MR contrast agents as a cargo within PRINT particles to complement the PET/CT results described in Figure 1.

With the growing demand for unique multifunctional composite materials for a range of advanced applications that require controlled optical, mechanical or electrical properties, there is a need for scalable fabrication processes that would allow for precise nanostructure control. PRINT is a viable approach for this type of fabrication as it provides complete tunability of the filler particle parameters: shape, size (nanometer to micron), orientation and composition. As the molded particles are in an initially non-aggregated state either in the mold or on a substrate, strategies can be employed to transfer the particles to a matrix without aggregating the particles. Using a layering approach, particles are uniformly dispersed in a polymer matrix to generate complex three-dimensional architectures, where particles cannot aggregate. Both polymer-polymer and polymer-ceramic composites have been generated using this technique, with particle inclusions ranging in size from 7 microns to 200 nm.